1. Field of the Invention
This invention relates to a structure of a fuel gauge for vehicles including automobiles, motorcycles and boats, and more particularly to a fuel gauge which utilizes fibre optical devices.
2. Prior Art
In modern industry, it is one of the most important considerations to have precise and reliable fuel gauge provided in vehicles. In achieving this object, a number of structure have been disclosed and practiced in the past.
Among them all, a float ball mechanism has been considered the most common and reliable. According to the float ball mechanism, vertical movements of the ball floating on the surface of the fuel are converted into rotational movements at the end of an arm connected to the ball. Such rotational movements may further be converted into electric signals which be displayed in a conventional visual manner.
For example, the movement of the float ball in a fuel tank in an automobile may be converted into a visual signal displayed on the surface of the dashboard of an automobile.
However, it has been recognized that the float ball mechanism frequently causes inaccuracy problems. Such problems commonly occur in the following circumstances:
(1) When a vehicle is moving:
Since the level of the fuel cannot be even, the float ball would not reflect the actual volume of the fuel in the tank. As a result, the measurement presented in a display would not be accurate. Typically a driver of an automobile often suffers from misjudgment of the fuel gauge caused this inaccuracy problem.
(2) When the float ball mechanism gets old:
It is perceptible as the mechanism being used for a certain period of time that the mechanical connections may become loose or deformed causing inaccurate movements.
Furthermore, the float ball mechanism cannot be free from a limitation in measuring the liquid content when it gets close to empty. More specifically, the lowest level measurable by the float ball would not represent the real empty level of the fuel content, since the bottom part of the ball beneath the fuel level reaches the lowest level before the fuel level gets to the real empty level.
As a result, it is not unusual that the operators could not fully rely on those gauges using the float ball mechanism.
Therefore, attempts have been made to build a fuel gauge which is more accurate and reliable. Some of these attempts are disclosed in the patents as follows: U.S. Pat. No. 3,713,338; U.S. Pat. No. 3,794,428; U.S. Pat. No. 4,450,722; U.S. Pat. No. 4,630,476, U.S. Pat. No. 4,440,022 and U.S. Pat. No. 4,156,149.
Among these patents, U.S. Pat. No. 3,713,338 discloses some unique features in that a set for fibre optical members vertically arranged is used to detect the level of the fuel. However, this system requires a rather complex structure, particularly in that first and second chambers separated by a flexible diaphragm and a transparent vessel connected to the first chamber are needed outside of the tank. According to this structure, it is the level of the light absorbing liquid contained in the transparent vessel that is measured by the optical members. In other words, this structure does not allow direct measurement of the fuel level in the tank to be taken resulting in more manufacturing cost and insufficient accuracy.